THE THIES PROCESS 

OF 

BARREL CHLORINATION. 

BY 

T. EGLESTON, Ph.D. 


Reprinted from the School of Mines Quarterly, No. 2, Vol. XI, 

January, 1890. 














«0 

*1 


[Reprinted from the School of Mines Quarterly, No. 2, Vol. XI.] 



THE THIES PROCESS OF BARREL CHLORINATION. 

BY T. EGLESTON, PH.D. 

# The pyrites containing gold resulting from the concentration of 
free milling gold-ores is usually treated by Planner’s process, 
which was introduced into Grass Valley, California, in 1858, by 
Mr. G. F. Deetken, and has been successfully practiced therefrom 
that time. Various modifications of it have, from time to time, 
been suggested. Mears proposed to use chlorine gas under press¬ 
ure of 30 to 40 pounds to the square inch, made in a generator 
outside of the barrel and pumped into it or produced inside the 
barrel by the use of a great excess of chemicals ; and while it was 
found that more gold was dissolved, the gain was more than com¬ 
pensated for by the expense of the machinery, the great cost of 
repairs, the trouble caused by the leakage of the gas and con¬ 
sequent loss of the chlorine and inconvenience to the men. 
Davis proposed to precipitate the gold with charcoal, but no 
special advantage resulted from it. The precipitation is slow, and 
the difficulty of burning such bulky material in a muffle and treat¬ 
ing the ashes before melting into a bullion, caused its abandon¬ 
ment. Mr. A. Thies, by whose advice the process was introduced 
at the Phoenix and Haile mines in North Carolina, and the Bunker 
Hill mines in Amador City, California, having been in charge of 
the Mears process for more than four years, found that he could 
work without pressure-pumps just as well as with them, as all the 
pressure necessary for the solution of the gold, could be generated 
within the barrel just as well and much cheaper than by costly 
machinery, and after making a long series of experiments, leaving 
out of the Mears process all but the barrel, and having modified 
that so that there were no joints liable to leakage, in fact, so that 
there was nothing but the bare lead-lined iron cylinder left of it, 
perfected the process which is now known as the barrel process, 
but should be really known as the Thies process, which has been 
introduced at the Bunker Hill mine in Amador City, California, 





140 


THE QUARTERLY. 


and at the Phoenix and Haile mines in North Carolina, where it 
has been working for several years very successfully. 

Through the courtesy of Mr. N. YV. Crocker, superintendent of 
the Bunker Hill mine, I had an opportunity to study this extremely 
interesting process at that mine. The details relating to the Haile 
and Phoenix mines have been forwarded to me by Mr. Thies. 
The Bunker Hill mine was located in 1852. It is situated \]/ 2 
miles north of Amador City. The vein dips at an angle ot 75 °, and 
varies from 3 to 25 feet in width. It has two inclined shafts, one of 
which is 800 feet long on the incline and 683 feet deep from the 
surface in a vertical line. The south shaft is 400 feet long on the 
incline and 345 feet vertically from the surface. The two shafts 
are 360 feet apart. The hanging is diorite and the foot slate. 
The ore is quartz and black slate, with 2 per cent, of sulphurets, 
and is worth $5 to $6 to the ton. It is crushed in Hendy’s modi¬ 
fication of the Blake’s crusher, which is run by a 4-foot Knight’s 
wheel under a pressure of 260 feet of water. The mill is run by a 
6-foot Knight’s wheel under a pressure of 270 feet. There is also 
a steam-engine to use in case of failure of the water. The mill 
has 40 stamps. The ore comes from the mine by a tramway, and 
is dumped on to grizzlies, and falls from there to a Hendy’s rock- 
breaker, 9 inches by 16, which does all the crushing. The move¬ 
ment is transmitted by iron arms from one end of the breaker to the 
other. The stamps weigh 850 pounds, the stem is 350, the shoe 
150, the boss 225. The tappit is of steel, and weighs no. The 
stamps make92 drops of 6 x / 2 inches, and each one crushes 2^ tons 
in twenty-four hours. The order of the drop is 1,5,2, 4, 3. The 
screens are No. 8, and are one-fourth of an inch angle slot, and last 
twenty days. The ore is amalgamated in the battery, and the splash- 
plate is arranged in such a way that the pulp falls on to an amal¬ 
gamated plate 8x4 inches, inclined away from the mortar at an 
angle of about 45°, then drops to another one of the same size in¬ 
clined towards it and then falls to the apron. This makes a fall from 
the screen to the first plate, and from the first to the second, and from 
the second to the sluice. The result of the constant impact is that 
little or no gold is found beyond these plates. The battery lip 
has two plates 8 inches long and 6 feet wide. The apron is 3 feet 
6 inches long and 4 feet wide. It has a grade of 1 ^ inches to 
the foot. It ends in a single sluice, 14 inches wide and 12 feet 
long,with a single silver-plated copper plate. This ends in a pointed 

ijy ■ I 

11 vwT Ac v 



THIES PROCESS OE BARREL CHLORINATION. 141 


box for each sluice. 90 per cent, of the gold is found in the battery, 
5 to 7 per cent, on the splash-boards and the rest on the plates. 
From the sluice the tails run on to Frues, which make 220 strokes. 
From the Frues the tails run on to duck sluices, of which there are 
50, 22 inches wide and 16 feet long, exactly resembling the Strakes 
of the Keystone mill. The pulp from this Strake concentration is 
treated in pans with wooden shoes. The water used in the milling 
and on the concentrators is 8 miner’s inches under a 4-inch head. 
The cost of milling is 60 cents. The number of men in the mill is 5 
and in the mine 70. Both miners and mill-men are paid $2.75. 
The cost of water for milling is $1.60, and for power $18.40, per day. 

The Bunker Hill and Phoenix works formerly used the Mears 
process, but were forced to abandon it because the cost of repairs 
was too great and it was found to be impossible to keep the 
chlorine from leaking, and the men refused to work when they 
were exposed to such corrosive fumes. There seems to be no 
doubt that the use of chlorine under very high pressure acts effi¬ 
ciently, and since its abandonment the tails are higher, but the differ¬ 
ence is not enough to pay for the extra trouble and expense. This 
seems, for the most part, to be owing to the use of dry ore and 
dry gas, no water having been previously used, but the whole dif¬ 
ference is not more than $2 per ton, which it seems impracticable 
to save on account of the difficulty of keeping the chlorine from 
leaking. All of the Mears process has therefore been abandoned, 
and as now conducted it does not bear much relation to the original 
process. 

The concentrates at Bunker Hill are 2 per cent, of the ore, and 
contain a trace of arsenic, antimony and lead. Their average 
value is $60 to the ton. They are roasted with I per cent, 
of salt in a reverberatory furnace with a revolving hearth at 
the fire-place end. It is 40 feet long and 12 feet wide on the 
outside, with walls 18 inches thick. The stationary hearth is 7 
feet wide, 18 feet long and 24 inches high, and has two working 
doors, one on each side of the furnace. They are 8x16 inches. At 
the end of the stationary hearth there is a drop of 6 to 7 inches. 
The ore then falls on to a horizontal revolving hearth 12 feet in 
diameter, with a discharge-hole in the centre. This part of the 
furnace is made of an iron shell lined with fire-brick. It is 24 
inches high to the crown of the roof, and 18 inches to the spring 
of the arch. The working door is 3 feet above the floor of the 


142 


7 HE QUARTERLY. 


roasting house. The bridge is 9 inches below the arch, and the 
grate-bars 18 inches below that, so that the fire-place and com¬ 
bustion-chamber together are 27 inches deep. This furnace is 
too small for any large output. The hearth revolves, by means of 
gear-wheels beneath it, at the rate of one turn per minute. The 
work consists in turning the concentrates over and bringing them 
from the centre to the circumference, and pushing them from the 
circumference to the centre. When finished, the charge is shoved 
from the centre, through the hollow axis of the hearth, into the 
cub below, and from there the roasted ore is removed by scrapers 
attached to the bottom of the pan and loaded into iron cars and 
carried in them to the cooling-floor. There are, in the furnace, 
three batches of 1100 pounds of ore. One is on the end of the 
hearth nearest the flue drying, the others being roasted. The 
charges are moved every eight hours. The same charge re¬ 
mains eight hours on the revolving hearth. To ascertain whether 
the roasting has been sufficiently prolonged to decompose all 
the sulphates, a small quantity of the hot charge is thrown into 
water, and a bright iron rod thrust into it. If there is any un¬ 
decomposed sulphate, the rod will be acted on; if not, the 
charge is ready for the barrel. The capacity of the furnace is 2 
tons in twenty-four hours. 0.25 per cent, of sulphur remains in 
the ore after roasting. It requires five-eighths of a cord of wood, 
at $6 per cord, to the ton. At the Haile mine, in North Carolina, 
a double reverberatory furnace is used; they have just erected a 
Spence furnace to roast the concentrates. 

The cooling-floor is of brick, and is on the same level as the 
charging-hole of the chlorinating barrel. The charge is generally 
made hot, but not sufficiently so to be burning to the hand. It is 
weighed and charged in iron wagons. The barrel charging-floor 
is of wood, in the centre of which is a hole 2 feet in diameter, into 
which an iron hopper fits. The barrel is on the floor below, and 
has a man-hole 12 inches in diameter, which is turned up under¬ 
neath this hopper. The barrel is of cast-iron or sometimes it is 
made of boiler plate, and is lined on the inside with lead, usually 
weighing 10 or 12 pounds to the square foot. All the joints are 
burned together when the lead is first put in. The lead used is 
one-quarter of an inch thick, and weighs 12 pounds to the square 
foot. After five years of use at the Phoenix mine, this lining shows 
no appreciable wear. The barrel is 4 feet in diameter outside and 


TRIES PROCESS OF BARREL CHLORINATION. 


H3 


40 inches inside, and 6 feet long outside and 54 inches inside. The 
heads are made of cast-iron with the trunnions cast on them, and 
are fitted to flanges on the body; these are fitted with tight and 
loose pulleys. The lining must be well put in and with great care. 
It is fastened at once by bolts to the outside, as it has been found 
very difficult, when repairs are required, to burn lead on which 
chlorine has acted. There were formerly in the barrel, on the 
bottom, partitions of lead 2 to 3 inches high, which make the 
charge rise and fall out as the barrel revolves, instead of simply 
rotating around on the bottom. This has been found to compli¬ 
cate the construction of the barrel unnecessarily and has been 
abandoned without any perceptible change in the work. When 
the chlorinating barrel is turned up, 135 to 140 gallons of water 
are introduced from a wooden barrel at the side of the hopper 
by a pipe. The exact quantity of water is ascertained by marks 
on the inside of the barrel, and as soon as empty it is filled again 
to be ready for the next charge. The water must be in sufficient 
quantity to allow the pulp to flow easily, but it must not 
be too thin. One ton of roasted sulphurets is now added 
through the funnel, it having been previously thoroughly mixed 
with 25 to 30 pounds of dry chloride of lime, which is the ordi¬ 
nary bleaching powder of commerce. This amount has been fixed 
on as the best, as it has been found that with a charge of 40 
pounds no better results were obtained. When, as in some cases 
in North Carolina, the ore contains copper, more bleaching pow¬ 
der has to be used. The water is added first, because if the dry 
ore was added and then the water the barrel would be more than 
full, as the two would not. mix, but the ore falls through the 
water, so that the barrel is filled up to 8 or 9 inches of the man¬ 
hole. What remains on its sides is then washed off the funnel 
with a little water. Thirty pounds of sulphuric acid at 66° B. are 
added after the rest of the charge is made. An excess of acid 
must always be used, so as to be sure to convert all the lime 
which remains on the hopper, into sulphate, and the funnel washed 
free of acid, and then it is removed. In North Carolina the water 
is put in first, then the ore, and then the acid. The charge which 
answers best at the Phoenix mine, where the ore contains copper, 
is 40 of bleaching powder and 50 of commercial sulphuric acid. 
At the Haile mine, where the pyrites is free from copper, the 
charge is 10 pounds of bleaching powder and 15 pounds of acid. 


144 


THE QUARTERLY. 


Half of each is used at the commencement, and after three hours 
rotation the rest. The rotation is continued until free chlorine is 
present. When the charge is in, a rubber is placed over the man¬ 
hole, and an iron plate over this, which is screwed down tight with 
a long lever as quickly as possible to prevent the escape of any 
chlorine from the barrel. The barrel is revolved at the rate of 12 
revolutions a minute for four hours. At first the whole charge of 
chemicals was made at one time. This was found not to work 
advantageously and now the charge is divided. Two charges are 
always made in a day. In North Carolina half the quantity re¬ 
quired to generate the chlorine is introduced at first, and the rest 
at the end of half the time of rotation, and the process continued. 
The time of the rotation of the barrel is from 4 to 8 hours, de¬ 
pending on circumstances. When an examination shows free 
chlorine present the operation is finished. It will not do to trust 
to pressure alone to determine the presence of chlorine in excess, 
for other gases are given off as well as chlorine, which would give 
a false indication if the operation was determined as finished by 
the pressure alone. A lead valve is arranged in the barrel, so that 
not only the pressure of an excess of chlorine gas, but its presence 
and the exact condition of the charge, can be ascertained at any 
time. Where examination shows that there is an excess of free 
chlorine in the barrel the pulp should be left in contact with it at 
least an hour before discharging. 

The barrel is surrounded for two-thirds of its height on both 
sides by a splash-box 18 inches wide, which ends in a trough 
which can be turned on to any one of the tubs. When the charge 
is finished the barrel is turned up. The chlorinator, wearing a 
respirator, as there is considerable pressure of gas, loosens the 
screw of the man-hole, so as to raise the rubber a little and allow 
the extra chlorine to escape for several minutes. He then removes 
the valve altogether, and with his hands turns the barrel down 
into the trough. The whole charge runs on to the filter, the bed of 
which is 6 inches in thickness. The filter is first flooded from below 
to the depth of 4 or 5 inches with water and the outlet stopped. 
This prevents the charge from below from packing as the ore falls 
on to it. The barrel is then washed out with a little water, and 
it is ready for a new charge. The trunnions of this barrel, which 
was originally made for the Mears process, were made hollow for 
the purpose of introducing the stationary goose-neck, through 


THIES PROCESS OF BARREL CHLORINATION. 


145 


which the pressure of the gas in that process, which was from 30 
to 40 pounds to the square inch, was made and measured. They 
were made too large in the first place, and are now very much too 
large. They have been stopped up with asbestos, as they are no 
longer used. In all the recently constructed barrels the trunnions 
have been cast solid. The difficulty with the barrel so con¬ 
structed was the leakage of the stuffing boxes for the goose¬ 
neck, which it was impossible to keep tight. Another and a 
greater one was the collapsing of the lead lining of the barrel 
from the exhaust, in the endeavor to collect all of the chlorine gas 
in the barrel which was not used in the chlorination, so as to use 
the gas in the next operation. Another was the fact that there 
was often pressure due to the evolution of other gases than chlo¬ 
rine, which were mistaken for it, and the fact that, from mistakes 
as to the pressure, the ore supposed to have been fully acted upon 
by the chlorine had often not been sufficiently treated, so that the 
tails had to be worked over. The barrel is run by a 30-inch 
Knight’s wheel. 

The time necessary to revolve the barrel is not quite fixed, ex¬ 
cept by the work of the furnace. The total cost of power is $\ 
in twenty-four hours, or $0.50 per ton. As the fu/nace is small 
the quantity to be treated is small. Double the quantity might 
be treated if there was sufficient pyrites to treat. Two hours 
with the Bunker Hill concentrates would answer for the chlori¬ 
nation as well as four. The barrel discharges into three filter- 
tanks, which are rectangular, 6 feet by 8, and 18 inches deep. 
They are lined with lead, and incline 1 inch toward the drain-hole. 
The filter in California is made in them as usual, of quartz pebbles, 
gravel and fine sand. To keep it in place and prevent its surface 
from becoming uneven, longitudinal slats \ ]/ 2 inches deep and 10 
inches apart, are used on the top. In North Carolina the bottom 
of the tank is first covered with perforated tiles which are covered 
with gravel and then sand. They have two outlets for discharging 
into the settling-tanks. When the barrel is entirely empty the 
stopper in the tank is removed and the charge is allowed to drain, 
and is then washed with clear water, as rapidly as possible, until no 
gold is left. To do this the barrel-charge is allowed to drain until 
the surface of the pulp is bare. The outlet is then closed and 
water is added until it stands 3 to 4 inches above the surface of 
the pulp ; this is then drained. The outlet is again closed and the 


146 


THE QUARTERLY . 


vat filled full of water, which will be from 9 to 10 inches deep. 
This is drained and the tails will then generally be clean. They 
must, however, be examined and the leaching continued if gold is 
present. The filtration is done very rapidly, but the time depends 
for the most part on the fineness of the ore. When the wash 
water contains chlorine but no gold, the tails will be clean. From 
250 to 300 gallons of wash water are required per ton of ore treated. 
In six hours from the time the roasted pyrites is charged in the 
barrel the tails are clean and the filter ready for a new supply of 
barrel-treated ore. 

The settling-tanks are round, and are called stock-tanks. There 
are three of these 8 feet in diameter and 4 feet deep. They settle 
in fourteen to sixteen hours, and are drawn into the precipitation- 
tanks, which are on a level below the bottom of the stock-tanks. 
The precipitation-tanks are 5 feet in diameter and 3 feet deep. 
In North Carolina they are 6 to 8 feet in diameter, and the same 
depth. They are quite large enough to hold all £he wash liquors 
of 3 tons of roasted ore. There are six of them. The ferrous sul¬ 
phate is siphoned into them. The solution must have a decidedly 
acid reaction, in order to be certain that all the lime has been con¬ 
verted into sulphate. Ferrous sulphate gives a bulky precipitate 
with neutral solutions of calcium chloride. The solution is stirred 
with a wooden paddle and the ferrous sulphate added in excess. 
When the gold is all down the ferrous sulphate is turned off, and 
the whole allowed to settle from forty-eight to seventy-two hours. 
The supernatant liquor is allowed to run out and a fresh charge 
introduced into the vat. The spent liquor is allowed to flow on to 
a sand filter covered with sacking. The sand is taken up once a 
year and chlorinated by itself. When copper is present in the 
ore the weak solution, after the precipitation of the gold, is run 
over old iron, and then goes to waste. The sulphurets treated 
assay $55. The tails assay from $3 to $3.50. Occasionally they 
go as low as $1. The gold is collected carefully, washed to re¬ 
move the iron salts, and melted as usual. When carefully done 
the bullion is from 990 to 995 fine. Sometimes it may go as low 
as 975. 

It is a matter of surprise, considering the time -and pressure of 
gas used, that this process does not bring the tails down as low 
as in the Mears process, where the roasted concentrates were 
moistened with only 15 to 20 gallons of water, whose only object 


THIES PROCESS OF BARREL CHLORINATION. 147 


was to prevent the roasted concentrates from dusting. The diffi¬ 
culty seems to be in the roasting. No salt was added in the Mears 
process, and the temperature of the roasting was much higher at the 
end. The explanation must be found in the roasting, as the wet gas 
does not explain the difficulty. No time, quantity of lime, or other 
change seems to affect the tails. The tails, when treated, are thrown 
into a trough in front of the. tanks and sluiced out. Only one cord 
of wood a day is used in roasting. The experience in these works 
has been that the tanks last best when the wood has been soaked 
in linseed oil, dried, and painted with tar or three good coats of 
white lead. The roasted sulphurets are worked up to 92 per cent, 
of their assay value. When, as they sometimes do, they contain 
twice their ordinary value, they are worked just as close, the 
tails in both cases never containing more than $3.50. When they 
were worked by Plattner’s process in the usual way the tails often 
contained as high as $7 a ton. The cost of this process, at Bunker 
Hill, per ton of roasted pyrites is given below : 

Roasting. 

Two roasters, at $3.25, . . . . . . $3.25 

Five-eighths cord of wood, at $6, ..... 3.75 

- #7.00 

Chlorinating. 


One chlorinator, at $3, ....... 1.5° 

Thirty pounds of bleaching powder, at 4 cents, . . 1.20 

Thirty-six pounds of 66 sulphuric acid, at 3^ cents, . 1.26 
Twenty pounds of salt, at ^ cent, . . . . .15 

Water-power, . . . . . . . . - 5 ° 

General expenses and loss, ...... 3 -°° 

-7.61 


Total for one ton of ore roasted and chlorinated, . . . $14.61 


The cost of doing this in North Carolina is very much less : 

Roasting. 

Four laborers for roasting 2 tons of ore, at $1, . . $2.00 

One cord of wood for roasting 2 tons of ore, at $1.25, .625 

-52.625 






148 


THE QUARTERLY. 


Chlorinating. 

$0.45 
0.50 
0.30 
0.30 

0.125 
0.20 
0.125 

-2.00 

Total for one ton of ore roasted and chlorinated, . . $4,625 

The success of this process is undoubtedly owing to the forma¬ 
tion of nascent chlorine in contact with ore, which is constantly 
being rubbed bright by the friction of the particles against each 
other and against the sides in the revolving barrel. In two years 
use of the process at the Haile mine, there have been no repairs. 
Under the conditions of the process it would be impossible for any 
coating forming on the particles of gold to remain on them, and if the 
gold is bright it is sure to be attacked, which might not be the case 
when the ore is treated in vats. The solution and filtration are 
done so rapidly that there is little chance for the gold dissolved, to 
be precipitated elsewhere than in the precipitation tanks. The 
advantages of this process are the small amount of space it occu¬ 
pies, the celerity of the operation, the high percentage of yield, 
the facility of ascertaining the exact condition of the charge at any 
time, and the very slight wear and tear. The only disadvantages 
are that a small amount of power is required to be used, which is 
not necessary in the ordinary Plattner’s process, and that more than 
ordinary care and intelligence are required to run it. 


Two laborers for 4 tons, at $0.90, . 

One chlorinator, at $2, ...... 

Forty pounds of bleaching powder, at 3 cents, 

Sixty pounds of sulphuric acid, at 2 cents, . 
Seventy-five pounds of sulphuric acid for ferrous sul¬ 
phate, at 2 cents, ....... 

Repairs, wear and tear, ... . . . 

Power, ...... . 
















X 



